Basis of Presentation - Additional Information (Detail) (USD $)	Apr. 27, 2013	Mar. 23, 2013	Jan. 26, 2013	Jul. 31, 2012	Apr. 28, 2012	Jan. 28, 2012	Jul. 31, 2011	Apr. 22, 2013 Asset Sale Agreement
Summary Of Significant Accounting Policies [Line Items]
Total dispute amount under asset sale agreement								$ 1,400,000
Accrued warranty costs	$ 2,800,000	$ 0	$ 1,075,000	$ 1,072,000	$ 1,083,000	$ 1,125,000	$ 1,140,000